H. William Johansen

A reappraisal of the order Corallinales (Rhodophyceae)

Articulated and non-articulated coralline algae were brought together in the family Corallinaceae in essentially its present-day circumscription by Decaisne in 1842. Since that time, this family ha...

Rocky shore turfs dominated by Corallina (Corallinales, Rhodophyta) in northern Japan

Three intertidal sites dominated by Corallina turfs were investigated in Hokkaido, Japan. The sites (A, B and C) differed in slope, wave exposure and length of time exposed to air during tidal cycles. Monthly samples were analyzed for frond morphology and other features. Site A, the most wave‐exposed site, was dominated by Corallina sp. X, an unknown species, and sites B and C by Corallina pilulifera Postels et Ruprecht. At the different sites the populations differed in conceptacle abundance, coverage by epiphytic Titanoderma corallinae (P. Crouan et H. Crouan) Woelkerling, Chamberlain et Silva, amount of contained sediment, numbers of axes per quadrat, numbers of branch fusions, branch entanglement, frond dryweight, frond length, amount of adventitious branching, numbers of epiphytes (exclusive of T. corallinae), and numbers of animal species. Ninety‐one animal species were recorded from the turfs. Corallina is affected morphologically by conditions inherent in its microhabitat, including desiccation, epiphyte loading and the abundance of herbivores.

ALIZARIN RED DYE AS A MARKER FOR MEASURING GROWTH IN CORALLINA OFFICINALIS L. (CORALLINACEAÈ, RHODOPHYTA)1

The vital stain alizarin red was incorporated into the calcified walls of incipient medullary cells of Corallina officinalis L. while they were being produced in a terminal meristem. After about 5 h the stained tier of medullary cells formed a red‐purple band from which additional growth could be measured in the field and in non‐agitated cultures. Alizarin red was also taken up by epithallial cells and one month after staining, plants in the field lacked stained epithallia, whereas those in culture retained some of the stain. Possibly the lack of water motion in culture reduced the epithallial sloughing that occurs in nature. Growth rates measured by this technique were approximately 1.4 mm per month in the field and 1.2 mm per month in culture and were not affected by alizarin red.

The diagnostic value of reproductive organs in some genera of articulated Coralline red algae

Clearcut differences exist between the reproductive organs of Corallina and Jania. Fully formed spermatangial conceptacles in Corallina have low ceillings and pronounced beaks whereas in Jania they have high ceilings and lack beaks. Fusion cells in carposporophytic conceptacles are thin and broad in the former genus and thick and narrow in the latter. Tetrasporangial conceptacles have less capacity in Jania than in Corallina and the fertile areas in young conceptacles cover a smaller area. Haliptylon is changed from group to generic status and Corallina subulata is transferred to this genus. Haliptylon is characterised by conceptacles similar in all known respects to those of Jania, but the branching is pinnate, as in Corallina. From the available evidence it appears possible that organisms having Corallina-type conceptacles diverged phylogenetically long ago from those having Jania-type conceptacles.

PATTERNS OF GENICULAR DEVELOPMENT IN AMPHIROA (CORALLINACEAE)

Two types of genicular development (designated Types I and II) are present in South African species of Amphiroa. Genicula of both types originate when medullary tissue near branch endings softens by decalcification. In Type I decalcification does not progress to the branch surface and the joint therefore does not become flexible until the cortex, which remains calcified, cracks and partly sloughs. This type occurs in all species of Amphiroa in South Africa except one, and possibly occurs in those in the rest of the world as well. In Type II decalcification continues centrifugally to the surface of the branch; this results in a geniculum comprising medullary and cortical tissue. As far as is known this type occurs only in Amphiroa ephedraea. Type I appears to be more primitive than Type II.

ONTOGENY OF SEXUAL CONCEPTACLES IN A SPECIES OF BOSSIELLA (CORALLINACEAE)1

The first evidence of conceptacle formation in male and female plants of Bossiella californica ssp. Schmittii is the secretion of a cap below the epithallium. Subsequent development involves the disintegration of the upper enucleate parts of cortical cells below the center of the cap concomitant with the growth of tissue surrounding these cells. Protoplasts in the lower parts of these cortical cells recover and become initials of reproductive cells. Differentiation of each initial in female plants results in a supporting cells bearing 1 or 2, 2‐celled carpogonial filaments, and in male plants results in a basal cell bearing 2 or 3 spermatangial mother cells which bud off spermatangia. Following fertilization, supporting cells fuse and form a broad, thin fusion cell from the upper surface of which gonimoblast (carposporangial) filaments arise.

Morphogenesis and evolution in the Amphiroideae (Rhodophyta, Corallinaceae)

Using light- and scanning electron microscopy of Lithothrix aspergillum and Amphiroa spp., homologies in vegetative anatomy and morphogenesis in the two genera are resolved. The genicula of these genera are functionally comparable non-homologous structures. The long-celled medullary tiers are developmentally equivalent in Lithothrix and Amphiroa as are the short-celled tiers, the latter remaining meristematic to produce cortical sheaths. In Amphiroa the boundaries of the cortical sheaths are manifested at the macroscopic level by transverse markings across thalli in terminal intergenicula, and at the microscopic level by overlapping or otherwise disrupted cortical cells. Thus an intergeniculum of Amphiroa is equivalent to many fused genicula and intergenicula of Lithothrix. The evolutionary implications of this homology are discussed.